1. Field of the Invention
The present invention generally relates to a method and apparatus for controlling a vacuum pump system.
2. Description of the Related Art
Semiconductor substrate processing is generally performed in process chambers having sub-atmospheric pressures. Vacuum pump systems are commonly utilized to achieve and maintain sub-atmospheric pressures within the process chambers. The vacuum pump systems are typically remotely located in a “grey area” or a “sub-fab” outside the clean room to prevent adverse affects on substrate processing.
Vacuum pump systems serving a typical process chamber generally have a pumping capacity in the range of 1600 l/min up to 25,000 l/min in order to satisfy the needs of typical substrate processing operations. Vacuum pump systems of this capacity generally consume up to about 6 kilowatts per hour of electricity. Further, vacuum pump systems are typically operated at a constant speed during system operation, while chamber pressure is controlled by gas flow, throttle valve and isolation valve actuation. Accordingly, vacuum pump systems are a significant source of power consumption in semiconductor processing systems, as well as other types of systems.
As a result, new approaches to reducing the power consumption of vacuum pump systems are constantly being explored. Reducing power consumption is desirable both for reducing the energy associated with maintaining sub-atmospheric pressures and for reducing the heat generated and subsequent cooling requirements of the vacuum system, the clean room and the facility. Additionally, conservation of energy is desirable for social, economic and environmental benefits.
One possible approach to conserving power is through the use of variable speed vacuum pumps. Typically, variable speed vacuum pump systems include a motor driver that operates to maintain one or more selected motor speed setpoint(s) proportional to a desired pumping speed. The motor speed setpoint(s) is determined according to the desired processing conditions. During operation, the pumping speed may be changed by altering the selected motor speed setpoint(s). By controlling the speed of the pump it is possible to slow the motor speed when a higher speed is not needed.
Integrating a variable speed pump system onto an existing semiconductor processing system may require substantial changes to the system control software. Making software changes to existing systems is both expensive and time-consuming, and may require tracking a number of different software versions across a variety of semiconductor processing system platforms. Therefore, there is a need for a vacuum pump system that reduces power consumption and may be integrated onto a wide variety of semiconductor processing systems with minimal changes to processing system control software.